Russian is not the hardest language in the world. It is much easier than Chinese or Japanese for instance. However, there are some real difficulties in Russian:

#1 The Declension System
This is the single most difficult feature of the Russian language if you need to talk or write. Words change their endings according to the function in the phrase. The system is riddled with exceptions, so learning the declensions matrix is not enough. This being said, if you listen or read a lot of material in Russian, the most usual flexions get in your ear and you won't have to think when you need to use them. But this makes the language more difficult to speak perfectly. Please note that Russians are very forgiving of foreigners making mistakes, so you can use your Russian even if it's not perfect yet.

#2 Pronunciation
This difficulty is overrated, as you can easily develop a pronunciation that is good-enough to get understood. But speaking perfectly takes quite a lot of exercise, especially with the "soft" consonants and sometimes endless strings of consonants in some words. Also, the letter "o", a very popular letter in Russian, can be pronounced "A" or "O", depending on its position in the word and where the stress falls. You will get this wrong all the time at first, saying things like "bard" when you mean "board" or "pole" when you meant "pal ". Deal with it.

#3 Perfective/Imperfective verbs
It is not very difficult to get russian verb endings right (complexity is between English and German). However, each russian verb has two forms, one for each "aspect". This means that for a continuous action (as inI am reading the article), you have one verb (chitatj) and for a finished action, another verb (prochitatj). Most of these verb pairs differ only by the addition of a prefix (???, ??, etc...) so you won't have too much trouble to learn them. However, using the correct "aspect" is a real challenge. If you get it wrong, you will sayI will read the article when you really meanI am reading the article.

Don't let this discourage you! Russian still is the easiest language among the languages reputed to be very hard. There are also many easy parts of learning Russian.